I have not read all of the comments so if this has already been mentioned I. apologize.
When I bought my first digital camera a photographer told me to think of the xd/sd card as a blackboard slate. You start out with a clean slate, you write on it, then erase, write again, erase and so on. Every time you erase the slate a hazy white film is left behind, so after awhile the slate becomes less readable. The same thing happens with the card. So, I take pictures for a period of time, usually a month, during this time I do not delete any photos from the card. When I'm ready to load to the PC I do it either from the camera via USB cable or the PC's card reader I don't think it matters either way. After all photos are on the PC I go thru them and delete the unwanted ones, when I'm satisfied with everything I format the card from the camera's settings not the PC. I have been using the same card since 2011 with no problems.